ORA-65179: cannot keep datafiles for a pluggable database that is not unplugged

SQL> drop pluggable database pdb2;
drop pluggable database pdb2
*
ERROR at line 1:
ORA-65179: cannot keep datafiles for a pluggable database that is not unplugged


SQL> drop pluggable database pdb2 including datafiles;

Pluggable database dropped.

SQL>